Electric power tool, in particular a grinding or polishing machine

ABSTRACT

An electric power tool is described, and which includes a housing in which a drive, a fan unit and an electronics device are accommodated, and wherein an air stream for cooling the drive to be generated with the aid of the fan unit through at least one air inlet opening and at least one air duct being formed within the housing, and wherein the air duct extends from the air inlet opening to the drive, and which allows a directed supply of air to flow to the drive, with the air inlet opening being arranged in an end region of the electric power tool.

The present invention relates to an electric power tool, in particular a grinding or polishing machine, comprising a housing in which a drive, a fan unit and an electronics device are accommodated. It is possible for an air stream for cooling the drive to be generated with the aid of the fan unit by ambient air being drawn into the housing through at least one air inlet opening. At least one air duct is also formed within the housing, the said air duct extending in the flow direction of the air stream from the air inlet opening to the drive and allowing a directed supply of air to the drive.

An electric power tool according to the preamble is generally a battery-powered (DC-powered) and/or a mains-powered (AC-powered) electric power tool, for example a grinding or polishing machine or the like.

Electric power tools of this kind have a housing in which components which generate heat as lost power are accommodated, for example the drive or the electronics device. A fan unit which can generate a cooling air stream is provided in order to dissipate the heat which is generated by the said components.

The power consumed by the electric power tool is limited by the heat building up within the housing, and therefore it is ensured that the electric power tool can utilize all the power available to it only given sufficient cooling. In addition, sufficient cooling also improves the service life of the machine components of the electric power tool.

However, it has been found in the prior art that undirected cooling of the drive and/or of the electronics device may be insufficient. DE 10 2007 000 290 A1 therefore discloses providing a targeted or directed supply of air with the aid of air guide elements which delimit a secondary flow path via which at least a portion of the undirected main air stream can be routed to the electronics device. In this case, the electronics device is arranged in an end section of the handle housing part which is averted from the drive housing part. An air stream is drawn into the housing with the aid of the fan device of the electric power tool via a plurality of housing slots and flows along a main flow path, which is delimited by the drive housing part, to the fan device. The air guide elements provided are substantially perpendicular to the main flow direction along the drive motor and guide a secondary stream into the housing of the handle part, the said housing being arranged substantially perpendicular to the drive housing.

A further problem which has been found in connection with ventilating an electric power tool arises from the fact that, particularly in the case of grinding or polishing machines, particles of dust or the like can be drawn in via the air inlet openings, and this may lead to damage to the power tool or at least have an adverse effect on the service life of the said power tool. For example, particles of dirt of this kind can come into contact with the electronics device and greatly limit the functioning of the electronics device over the course of time. In particular, electrically conductive particles of dirt, for example metal dust or particles of dirt from iron-containing metals, can accumulate on the electronics device or the electric motor and lead to undesirable current flashover within the electronics device or the electric motor.

In order to solve this problem, EP 1 016 504 A2 discloses not arranging the air intake slots in the region of the handle switch of the electronics device, as in conventional electric power tools. The intention of this is to prevent soiling of the handle switch and any adverse effect on the functioning of the said handle switch. To this end, the housing of the electric power tool is of multi-part design and comprises a gear mechanism housing, a motor housing and a handle housing, these housings being arranged one behind the other. The handle housing, in which the handle switch and the major portion of the electronics device are accommodated, is separated from the motor housing by intermediate walls. The air intake slots for drawing in the cooling air are made on the motor housing which is connected in front, and therefore no part of the electronics device, in particular the handle switch, comes into contact with the cooling air.

An electric power tool according to the preamble is finally disclosed in DE 10 2006 038 756 A1, in which a device for generating a cooling air stream is provided. At least one rigid and/or flexible air duct is arranged in the housing of the electric power tool, with one end of the air duct facing the device for generating a cooling air stream and the other end of the air duct facing the component which generates heat. The air duct then conducts and distributes the air stream in order to cool the heat source in the form of the electric motor.

The air ducts are made up of a plurality of individual parts which are firmly flange-connected to one another. The said individual parts are then inserted into the half-shells of the housing during assembly of the electric power tool.

However, one disadvantage of a design of this kind can be, in particular, the complicated design of an air duct by one or more separate components which have to be able to be inserted into the housing. It is therefore necessary, for example, to provide fastening points on the housing, it being possible for the individual parts to be fitted to the said fastening points. It is also possible, particularly in the case of a flexible hose part, for the hose wall to be damaged during assembly, this resulting, for example, in additional post-processing steps and corresponding costs.

It is therefore an object of the present invention to cool the drive in as simple and efficient a manner as possible while at least reducing the known disadvantages.

This object is achieved by an electric power tool which comprises a housing in which a drive, a fan unit and an electronics device are accommodated, it being possible for an air stream for cooling the drive to be generated with the aid of the fan unit by ambient air being drawn into the housing through at least one air inlet opening, and with at least one air duct being formed within the housing, the said air duct extending in the flow direction of the air stream from the air inlet opening to the drive and allowing a directed supply of air to the drive. Furthermore, the air inlet opening is arranged in an end region of the electric power tool which, when a workpiece is being processed with the electric power tool, is averted from the workpiece which is to be processed. In addition, the housing is of double-walled design with a housing inner wall and a housing outer wall, which is at a distance from the said housing inner wall, at least in sections, with the air duct being delimited by the housing outer wall and the housing inner wall.

An air duct of this kind allows a direct supply of air starting from the at least one air inlet opening to the drive which is to be cooled. In principle, a single air inlet opening with a single air duct can be provided in accordance with the present invention. However, at least two air inlet openings are preferred, with each air inlet opening having an associated air duct.

On account of the air inlet opening or openings being arranged in an end region of the electric power tool which, when a workpiece is being processed by the electric power tool, is averted from the workpiece which is to be processed, the risk of soiling by particles of dirt which are contained in the air is already considerably reduced. The double-walled design of the housing in the region of the air duct with a housing outer wall and a housing inner wall, which is at a distance from the said housing outer wall, also makes it possible for a duct for a directed supply of air to be provided in as simple and cost-effective a manner as possible. The risk of unintentionally adversely affecting or damaging the duct walls during assembly of the electric power tool is considerably reduced in this way.

Provision can further be made for the electronics unit to be accommodated in the housing in such a way that it is separated from the air duct by the housing inner wall at least in sections, that is to say that it is accommodated in the housing within the space which is delimited by the housing inner wall. The housing inner wall particularly advantageously delimits a substantially closed chamber which is accommodated at least in sections within the housing outer wall. On account of a design of this kind, the electronics unit, which is accommodated in the housing within the housing inner wall, is “encapsulated” by the housing inner wall. Even when the housing inner wall does not form a completely inherently closed chamber, the directed air stream is routed past the electronics unit between the housing inner wall and the housing outer wall, and therefore particles of dirt which are contained in the cooling air do not come into contact with the electronics unit.

The embodiment in which the housing inner wall delimits a substantially closed chamber is particularly advantageous since it obviates the need to provide an encapsulated electronics device of this kind as has become conventional practice (encapsulated switch) in some cases. As a result, electronics components which are more cost-effective can be used for the electronics device without the risk of a reduced service life of the electronics device.

Furthermore, the housing outer wall can be in the form of a casing surface of a substantially cylindrical body which forms a handle part of the electric power tool at least in sections. In the case of a design of the housing of this kind, the said housing is of comparatively simple and cost-effective construction and extends along a longitudinal axis. The individual components, that is to say, for example, the electronics device, the drive and the fan unit, are usually arranged one behind the other within the housing. A drive shaft with a tool holder extends out of one end of the housing, it being possible to connect a tool of any kind, for example a grinding or polishing disc, to the said tool holder. The handle part of the electric power tool is designed to be grasped by one or two hands of the user. The lower the restrictions in respect of the intended handle region of the handle part, the less complicated it is for a user to handle the electric power tool since the said user does not have to pay attention to where on the housing region he can hold the power tool and where he should not.

The at least one air inlet opening can be formed at an end face of the housing by the space between the housing outer wall and the housing inner wall. In a design variant of this kind, the housing is not completely closed at the end face by the housing outer wall but is open at least in the region of the air inlet opening. In this case, the space is defined as that area which is delimited by the distance between the housing inner wall and the housing outer wall.

Furthermore, provision can be made for the air inlet opening or air inlet openings to have at least one, preferably a plurality of, supporting ribs which are substantially parallel to one another. The said supporting ribs can also extend between the housing outer wall and the housing inner wall in order to support the said walls against one another. In the case of the housing being produced from a comparatively soft material, for example from a plastic which can be deformed under a low action of force, this prevents the user from undesirably closing the air inlet opening by deforming the housing outer wall as a result of holding the power tool too tightly. It may be also be expedient, if appropriate, for the at least one supporting rib to extend along the entire air duct in the flow direction of the air stream.

Provision can further be made for the housing outer wall to project beyond the at least one air inlet opening at least in sections. In this embodiment, the housing outer wall does not terminate flush with the at least one supporting rib or with the supporting ribs of the at least one air inlet opening but projects beyond them (in a direction away from the tool of the electric power tool). This prevents the user from unintentionally closing the at least one air inlet opening with his hand (for example with the heel of the hand) when he grasps the handle part of the electric power tool.

In order to make production and assembly as simple as possible, the housing is of multi-part design and comprises at least two half-shells. The so-called pot structure, in which the housing has a pot-like frame to which the two half-shells and possibly further housing parts can be fitted, is particularly preferred in this case.

The electric power tool can comprise, as a drive, an electric motor having a collector and having means for making electrical contact with the collector, with the air duct conducting an air stream which is directed to the means for making electrical contact with the collector. Means of this kind for making electrical contact with the collector can comprise, for example, carbon brushes or the like.

Finally, the present invention also relates to a housing for an electric power tool having the features of Claims 1 to 10.

The invention will be described below with reference to the appended Figures which illustrate a preferred embodiment of the invention. A person skilled in the art will expediently also consider the features disclosed in combination in the drawing, the description and the claims individually and combine them to form expedient further combinations.

In the drawings:

FIG. 1 schematically shows an isometric view of an electric power tool according to the invention;

FIGS. 2A and 2B schematically show a plan view and, respectively, a detailed view of the electric power tool according to the invention as per FIG. 1; and

FIG. 3 schematically shows a housing shell of the electric power tool according to the invention as per FIGS. 1, 2A and 2B.

FIG. 1 shows an electric power tool according to the invention which is provided, in general, with the reference symbol 10.

The electric power tool 10 comprises a tool-side output drive 12 and a handle part 14 which is connected upstream as viewed along a longitudinal axis L. The handle part 14 is formed on a housing 16 which comprises a plurality of housing parts 16 ₁ and 16 ₂, with the housing part 16 ₁ being in the form of a housing pot with a handle section 36A and a fastening section 36B on which two half-shell-like housing parts 16 ₂ can be mounted. In FIG. 1, only one such shell-like housing part 16 ₂ is fitted in the lower region, while the upper region shows the fastening section 36B and the components of the electrical power tool 10 which are accommodated in the said fastening section.

It goes without saying that it is also possible for the housing 16 to be formed by a plurality of housing parts which do not necessarily have to be in the form of a half-shell or in the form of a pot.

A drive, which is in the form of an electric motor 20 (only indicated in FIG. 1) is also accommodated within the housing 16, it being possible for the said drive to be activated and deactivated by means of a sliding switch. To this end, the sliding switch has a switching element 18 which can be manually operated by a user. The switching element 18 is, as clearly shown in FIG. 1, arranged in the handle region of the electric power tool 10 on the outer circumferential surface of the housing 16. An arrangement of the switching element 18 in this way allows simple and uncomplicated handling for a user since the said user can switch on and switch off the electric power tool 10 with the aid of the switching element 18 without having to let go of the handle part 14 of the said electric power tool.

The drive of the present electric power tool 10 is, as mentioned above, in the form of an electric motor 20 and comprises, as is customary, a rotor, which can be rotated about the longitudinal axis L and is firmly connected to a rotor output shaft (not illustrated), and also a stator (not illustrated) which at least partially surrounds the rotor. An air gap is usually formed between the rotor and the stator of the electric motor 20 on account of the geometry of the stator. This air gap allows the electric motor to be ventilated and, in this way, reduces power losses from the drive due to overheating.

The rotor output shaft forms a drive connection with a driven shaft 22. The said driven shaft is centrally accommodated in an attachment with a substantially cylindrical housing 22A and has a tool holder 22B for holding an associated tool (not illustrated) at its free end.

A gear mechanism (not illustrated) can also be provided between the output of the electric motor 20, that is to say the rotor shaft, and the driven shaft 22, the said gear mechanism being accommodated in a corresponding housing 34 in the illustrated embodiment. A gear mechanism of this kind allows the torque which is transmitted by the motorized drive and its driving shaft to the output 12 to be stepped up or stepped down.

As can be seen in FIGS. 1 to 2B, a switching rod 30 is provided as a switching element of the sliding switch, the said switching rod being connected to the switching element 18 and being used to switch on and switch off the motorized drive. To this end, an electronics unit 32 is additionally provided, the said electronics unit interacting with the switching rod 30 and supplying power to the electric motor 20 only when the switching element 18 is in a corresponding on-position. To this end, the electronics unit 32 can have, for example, a pressure switch which is prestressed in a position in which the electronics unit 32 does not supply power to the motorized drive 20 by a compression spring which is integrated in the pressure switch. In order to switch on the motorized drive 20 with the aid of the activation unit 32, it is therefore necessary to push the pressure switch in the direction of the motorized drive 20 against the action of the integrated spring. In this case, the switching rod 30 takes on the task of transmitting a translatory displacement of the switching element 18 to the pressure switch along the longitudinal axis L.

In the illustrated embodiment, the electronics unit 32 is connected to a power supply system via a cable connection. However, as an alternative, power can be supplied with the aid of a rechargeable battery which can be attached to or is integrated in the housing 16.

In the illustrated embodiment, the electric motor 20 is connected to a fan unit, which is in the form of a fan impeller 26, in such a way that a rotary movement of the rotor shaft results in a rotary movement of the fan impeller 26. The fan impeller 26 is formed in a conventional manner in such a way that an air stream is generated by a rotary movement of this kind, with a suction space being produced within the housing 16. The drawn-in air is discharged to the outside via air outlets 38 in the gear mechanism housing 34, as indicated by the arrow designated LU. The housing 16 of the handle part 14 additionally has air inlet openings 68 on its end face which is averted from the output 12, ambient air being drawn into the housing 16 through the said air inlet openings, as indicated by the arrow designated LU.

FIGS. 2A and 2B show a plan view of the electric power tool 10 according to the invention as per FIG. 1, with FIG. 2B illustrating a detailed view of the detail designated B in FIG. 2A. FIG. 3 also shows a plan view of one of the housing shells 16 ₂.

The first housing part 16 ₁, which is in the form of a pot, has a fastening section 36B next to its holding section 36A (on the left-hand side in FIG. 2A), which forms a handle area, it being possible for two half-shell-like housing parts 16 ₂ to be fitted to the said fastening section. In order to axially secure the housing shell parts 16 ₂, fastening recesses 48 are provided in the region of the fastening section 36B, it being possible for corresponding fastening projections 46 of the housing shell parts 16 ₂ to engage in the said fastening recesses (cf., for example, FIG. 3).

Two air ducts 66 (at the top and at the bottom in FIGS. 2A to 3) are formed in the housing 16, the said air ducts each being delimited by a housing outer wall 40 and a housing inner wall 50. When the two housing shells 16 ₂ are connected to one another, the housing outer wall 40 is in the form of a casing surface of a substantially cylindrical body which forms a rear section of the handle part 14 of the electric power tool 10.

In addition to the fastening projections 46, each of the housing half-shells 16 ₂ has special connection geometries which ensure that the two housing shells 16 ₂ are exactly aligned with one another when they are connected to one another. Therefore, the lower housing shell 16 ₂ (shown in FIGS. 2A to 3) has first recesses 54 and second recesses 56 in which corresponding, for example peg-like, projections of the upper housing shell (not shown) can be accommodated. Furthermore, screw receptacles 52 are formed at the first recesses 54, the said screw receptacles running concentrically to the first recesses 54 and allowing fastening screws for connecting the housing half-shell parts 16 ₂ to be held. Furthermore, a cable recess 72 is provided in the end face of the two housing shell parts 16 ₂. In the case of the shown embodiment, an electric cable (not illustrated) to the electronics unit 32 can extend through the said cable recess. Furthermore, a groove 42 and corresponding projections (not illustrated) are provided on the respectively other housing half-shell in order to align and stabilize the housing outer wall 40 in the connecting region of the housing shell parts 16 ₂.

A special feature of the present invention can be seen in that the housing inner walls delimit an inner housing chamber in which the electronics unit 32 is accommodated. In the illustrated embodiment, the housing inner walls 50 extend inwards from the inner casing surface of the housing outer wall 40, and therefore this inner chamber for the electronics unit 32 is delimited both by the housing inner walls 50 and also by the housing outer wall 40. However, as an alternative, it is also feasible for the housing inner wall 50 to likewise form a circumferential casing surface, which is surrounded by the housing outer wall 40 at least in sections, when the housing shells 16 ₂ are in the assembled state.

The design of an inner housing chamber of this kind results in encapsulation of the electronics unit 32 which is accommodated in the said housing chamber and is protected by the surrounding housing walls against coming into contact with a drawn-in air stream and any particles of dirt which may be contained in the said air stream. In the direction towards the electric motor 20, this inner chamber is delimited by an additional wall 60 which has a recess 62 for the switching rod 30 (cf., for example, FIG. 3).

The housing half-shells 16 ₂ and also the housing pot 16 ₁ can be produced in a conventional manner from plastic, it being possible for these to be produced, for example, by means of injection moulding. In order to stabilize the housing inner walls 50, supporting ribs 64A and 64B can be moulded onto the said housing inner walls in the process.

The air inlet openings 68 are arranged in an end region of the housing 16 and are formed by the gap between the outer housing wall 40 and the housing inner walls 50. In order to mutually support the housing walls 40 and 50 and in order to prevent relatively large particles of dirt from being able to be drawn into the housing 16, a large number of supporting ribs 70 are arranged between the housing walls 40 and 50. These supporting ribs are aligned substantially parallel to one another and in each case extend from the housing outer wall 40 to the adjacent housing inner wall 50.

As is clearly identifiably shown in the Figures, the housing outer wall 40 is formed in the end region with a projection 44 in relation to the supporting ribs 70. This projection is used to considerably minimize the risk of the air inlet openings 68 being undesirably closed by the hand of a user, even when the user holds the handle part 14 of the electric power tool 10 in its end region.

The air ducts 66 extend from the air inlet openings 68 to the contact-making means 28 of the electric motor 20 which are usually in the form of carbon brushes which are fastened to a corresponding spring. The special design of the air duct 66 makes it possible for air to be supplied to the components of the electric motor 20 in a directed manner, the said components being subject to particularly pronounced development of heat on account of their continuous sliding contact with the collector of the electric motor and the heat of friction produced in the process. 

1. An electric power tool, and in particular a grinding or polishing machine, comprising: a housing in which a drive, a fan unit and an electronics device are accommodated, and wherein an air stream for cooling the drive is generated with the aid of the fan unit when ambient air is drawn into the housing through at least one air inlet opening, and wherein at least one air duct is formed within the housing and extends in the flow direction of the air stream from the air inlet opening to the drive, and which allows a directed supply of air to the drive, with the air inlet opening being arranged in an end region of the electric power tool which, when a workpiece is being processed with the electric power tool, is averted from the workpiece which is to be processed, and wherein the housing of has a double-walled design with a housing inner wall and a housing outer wall, which is at a predetermined distance from the said housing inner wall, at least in sections, with the air duct being delimited by the housing outer wall and the housing inner wall, and wherein the housing has a multi-part design which includes at least two half-shells.
 2. An electric power tool as claimed in claim 1, and wherein the electronics unit is mounted in the housing in such a way that it is separated from the air duct by the housing inner wall at least in part.
 3. An electric power tool as claimed in claim 1, and wherein the housing inner wall at least partially delimits a substantially closed chamber which is at least partially accommodated within the housing outer wall.
 4. An electric power tool as claimed in claim 3, and wherein the housing outer wall is in the form of a casing surface having a substantially cylindrical body which forms, at least in part, a handle part of the electric power tool.
 5. An electric power tool as claimed in claim 4, and wherein the air inlet opening is formed at an end face of the housing and is defined by the space between the housing outer wall and the housing inner wall.
 6. An electric power tool as claimed in claim 5, and wherein the drive comprises an electric motor having a collector and a means for making electrical contact with the collector, and wherein the air duct conducts an air stream which is directed to the means for making electrical contact with the collector.
 7. An electric power tool as claimed in claim 6, and wherein the air inlet opening has a plurality of supporting ribs which are substantially parallel to one another.
 8. An electric power tool as claimed in claim 7, and wherein the supporting ribs extend between the housing outer wall and the housing inner wall in order to support the said walls against one another.
 9. An electric power tool as claimed in claim 8, and wherein the housing outer wall projects beyond the respective supporting ribs at least in sections.
 10. (canceled) 